The present invention relates to a method for directing a desired amount of gas under the liquid surface in a solution reactor, preferably into its bottom part, for dispersing it into small bubbles, for mixing the bubbles as effectively as possible into a suspension of a pulverous solid and a liquid, and for producing in the mixed gas-solid-liquid suspension a strong, suspension-maintaining flow field which is directed downwards in the center of the reactor and upwards along the sides of the reactor. A gas flow directed from below a so-called gls-mixer according to the invention towards its center spreads radially outwards towards the mixer blades. Owing to vertical dispersion blades located at the edges of a circular plate attached on a horizontal plane to the axis, the gas is dispersed into small bubbles under the effect of the strong turbulence field produced by the rotational velocity of the mixer. The small bubbles formed are mixed with a solid-liquid flow in the blade-free area at a point downstream of the said dispersion blades, whereafter the outer, depressing baffles of the gls-mixer produce subsequent dispersion and force the formed suspension towards the lower part of the reactor and from there further upwards along the sides.
The mixer according to the invention is called a gls-mixer, a name which is derived from the operating principle of the mixer: gas is directed under a mixer in which it is dispersed and thereafter mixed with a liquid and a solid.
There are good and practicable methods for mixing a pulverous solid with a liquid to form a good suspension or to disperse a gas in a liquid. These have been described in the literature, for example in Ullmanns Encyklopadie der technischen Chemie, Band 2, pp. 260-281; the references below are to this literature reference.
One example of the mixing of a pulverous solid with a liquid consist of simple so-called pitch-blade mixers having a blade angle of 45.degree. (Ullman, p. 261, Abb 3, g); having a depressing effect, these mixers produce a flow which is downward in the center of the reactor and upward along the sides, and simultaneously produce turbulence important for the reactions.
There are also standard methods for dispersing a gas in a liquid;
A nozzle or several nozzles from which the gas discharges, thereby forming small bubbles. PA1 in a turbine mixer (Ullman, p. 261, Abb. 3, a) having vertical blades, gas directed under the mixer comes within the area of influence of the mixer and is dispersed into smaller bubbles the greater the power used in the turbine. PA1 Gas is also dispersed using so-called self-suction cross-pipes (Ullmann, p. 276, Abb 19), i.e. the gas space branches out from the lower end of a hollow shaft, most commonly into four pipes which are open at their tips. Owing to the underpressure produced in the gas space by the rotating cross-pipe the gas is discharged and dispersed into bubbles in the liquid space in the reactor. It should be noted that, when the temperature of the solution rises, the vapor pressure also rises, whereby the effect of the underpressure decreases.
However, the matter becomes more complicated when it is necessary simultaneously to disperse a gas effectively into small bubbles and, in addition, to maintain a pulverous solid in good suspension in a liquid. None of the methods described above is capable of simultaneously satisfying both these requirements sufficiently well, especially if the solid is coarse-grained and the density of the slurry is high.
The object of the present invention is to direct gas under the surface in a solution reactor, preferably into its lower part, to disperse it into small bubbles, to mix the bubbles as effectively as possible into a suspension of a pulverous solid and a solution, and to produce in the mixed gas-solid-liquid suspension a strong, suspension-maintaining, tubulent flow field which is downward in the center of the reactor and upward along its sides.